Have you Ever Started a New Position and Realized you were Totally Wrong for It?

Yes - the downside is that you have to spend time explaining to future recruiters why there is a Gap on your resume if you decide not to put that position on your resume.

It is the company's fault from my experience,

-Whether it was their overstatement or understatement of the problem they hired you to solve that caused the wrong fit, or

-Their discovery that you don't fit quite their culture, or

-Because your values don't align with those of the executives.

Employees should not be burdened with the responsibility for the bad hire. If you find out you are the wrong person for whatever reason, it was the company that did not do its job during the hiring process.

If you are not willing to stick it out through the 3 years it will take to put a reasonable block of time on your resume before jumping ship, you will be explaining that one for quite some time to come.

Be sure you get a reference in writing. You can try to negotiate a severance on your way out. Have a good story for the next round of interviews.

I have had this happen twice in a long career of senior executive positions. I was hired as CFO of a well funded internet service portal, in retrospect as "window dressing" for an IPO (I had been CFO in two prior IPO's). Withing a few months I uncovered financial misdealings on the part of the CEO and his brother and I immediately resigned. He later was indicted, convicted and sent to federal prison. If anything it was a plus in my career as demonstrating character and integrity.

The other time was entirely my fault in not having done enough personal due diligence to understand what was really expected of me. This emerged within my first week in the position and I met with the CEO and we parted on a friendly basis after one week. I do not list either of these on my resume as the gaps were short and I found another position in short order following both incidents. I do discuss them openly however if the situation merits.

OMG yes and hopefully only once. I started at a position that looked like a great fit. After three days I went to the HR person who was in the office and asked why she had not told me about the real working conditions. She said "how could I both my boss and the boss' boss were in the interview. I updated my resume. When I had my three month review they asked me how it was going and I said. 'awful'. We parted as friends. But I VOW that if i have that pit in my stomach about a job I will take longer to make the decision. I went on to be CEO of a company that I loved right after that.
How I have handled it? I have been totally honest with this short period of employment. It is an indication of resiliance and learning that you can make something good out of it. I am also much more diligent in evaluating a company I consider.